Field of the Invention
The present invention relates to the field of microwave heating. In particular, the present invention relates to a microwave heating apparatus equipped with a rotatable antenna for providing an improved crisp function.
Description of the Related Art
The art of microwave heating involves feeding of microwave energy into a cavity. Although the basic function of a microwave oven is to heat food by dielectric heating, microwave ovens have been developed to include additional kinds of cooking capabilities, such as e.g. a crisp or browning function, thereby enabling preparation of various types of food items and providing new culinary effects.
An example of such a microwave oven is for instance described in U.S. Pat. No. 5,268,546 wherein the microwave oven comprises browning means. The browning means includes a layer of ferrite material for absorbing microwave energy and generating heat and a metal browning plate in contact with the layer of ferrite material for browning food. For supplying microwaves to the oven cavity, an input opening is provided at the bottom of a side wall of the cavity such that polarized microwaves propagate between the cavity bottom and the browning means. As a result, a high amplitude standing wave is formed in the space comprised between the metal surfaces of the cavity bottom and the browning plate and the layer of ferrite material becomes hot due to microwave absorption. As the microwaves are fed from a side wall of the cavity, a drawback of such a prior art microwave oven is that the heating of the ferrite of the browning means is not very uniform and the crisp function suffers from unevenness.
Reduction of the unevenness of the crisp function may be obtained by rotation of the browning means or browning plate (in the following, no particular distinction is made between a crisp plate and a browning plate and reference to a crisp plate could equally be made to a browning plate and vice versa). For this purpose, the browning plate is preferably of a circular shape and fitted to be carried by a rotating bottom plate in the microwave oven. Although a satisfying crisp function may be provided by such a technique, a drawback is that the user is limited to use containers that can be rotated inside the cavity, thereby putting rather severe limits on the container size and shape. In addition, the design of the cavity itself is limited since browning functions provided according to such prior art techniques (i.e. based on side wall feeding at the bottom of the cavity) are sensitive to both the cavity dimensions and the position of the port feeding the microwaves at the side wall.
Thus, there is a need for providing alternatives and/or new devices that would overcome, or at least alleviate or mitigate, at least some of the above mentioned drawbacks.